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A series of laboratory large-scale model tests were conducted on piled raft founded on sand with different compaction levels. The numbers of piles are 1, 4, 5 and 9. All the piles are 40 cm in length and the slenderness ratio is 20. In these tests, the variation of load improvement ratio (LIR), load-sharing ratio (αp) and settlement ratio (SR) are reported for different relative densities and number of piles. Moreover, the variation of ultimate bearing capacity of piled raft system was investigated for different conditions. Results showed that LIR ratio will be more noticeable in loose state in comparison to dense sand, and also increasing the number of settlement reducing piles proved to decrease the SR values or increasing the SIF values in other words. In the end, a sensitivity analysis was performed to investigate the influence of each parameter in affecting the performance of the piled raft system. Based on the sensitivity analyses, relative density of soil was proven to be the most effective parameter in comparison to the number of piles. Finite element analyses have also been performed using the ABAQUS software. The numerical results from the FEM were first validated with the experimental results and then parametric study was carried out to investigate the effect of load eccentricities. It was shown that the ultimate bearing capacity of the piled raft foundation decreases significantly with an increase in the load eccentricity.

Stone column technique has been successfully applied for the foundation improvement. A rigid box with dimensions of 1.5 × 1.5 × 1.2 m equipped with a jacking-pump system was used to loading the stone column reinforced bed. Laboratory tests are carried out on stone columns with 6.3 cm diameter and different patterns surrounded by loose sand. The parameters varied in this experimental and numerical investigation are length, diameter and number of stone columns. The number of stone columns in these tests are 4, 5 and 9 and lengths of stone columns are 30, 40 and 50. A 40 × 40 × 2 cm steel plate is used as the model foundation. In these tests, the variation of bearing capacity ratio (BCR) and settlement reduction factor (SRF) are reported for different length and number of stone columns. The results show that by increasing the number and length of stone columns, BCR value will increase and SRF value will decrease. Finite-element analyses have also been performed using the ABAQUS software. The numerical results from the FEM were first validated with the experimental results and then some parametric analyses were conducted to investigate the effect of stone column diameter.

Soil reinforcement is an old and still efficient technique in improving soil strength and stiffness properties. Current paper aims at quantifying the effects of different inclusions on mechanical behavior of fiber-reinforced cemented soil. An experimental program was conducted to study simultaneous effects of randomly oriented fiber inclusions and cement stabilization on the geotechnical characteristics of fly ash-soil mixtures. Chamkhaleh sand, polyvinyl alcohol (PVA) fiber, cement and fly ash with some water were mixed and compacted into large scale direct shear apparatus with three equal layers. PVA fibers were randomly distributed in three compacted layers at predetermined weight contents. Direct shear tests were carried out on fly ash-soil specimens prepared with different cement, fly ash and polyvinyl alcohol contents, and 7 different curing periods. Results show that cement increases the strength of the raw fly ash-soil specimens. The fiber inclusion further increases the strength of the cemented and uncemented soil specimens and transforms their brittle behavior to ductile behavior. The fiber reinforcement and distribution throughout the entire specimen results in a significant increase in the strength of fly ash -soil- cement mixtures.